Conventionally, a technology of a supercharged engine provided with an emission control device is known (for example, Patent Document 1).
With a conventional supercharged engine, a permitted temperature of exhaust gas is sometimes set low from the standpoint of reducing fuel consumption.
In the case of providing such a supercharged engine with an emission control device (SCR system) for adding a reduction agent, such as urea water, to exhaust gas and reducing nitrogen oxide in the exhaust gas by a catalyst, the temperature of the exhaust gas may not rise to the activation temperature of the catalyst, and the efficiency of the catalyst reaction of the emission control device may be reduced.
Accordingly, the specifications of the supercharged engine have to be changed to achieve a balance between the engine performance and the exhaust gas temperature.
That is, the specifications of the supercharged engine have to be changed according to the type (activation temperature) of catalyst to be used by the emission control device, and the temperature of the exhaust gas has to be adjusted such that a temperature of the exhaust gas necessary to activate the catalyst used by the emission control device may be achieved. However, there are, for example, the following demerits: (1) it is necessary to receive regulatory certification regarding exhaust gas for each change in the specification, (2) a development test has to be conducted for each change in the specification, and the number of steps of development testing is increased, and (3) changed specifications would involve different parts, and the number of parts to be managed is increased.